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Johnny Pneumatic · 24th September 2004, 08:23 AM

I'm quite fascinated by ciliated microorganisms. They are like little jet fighters underwater. Question: Can cilia be scaled up and still work like they do at micrometer scales? For instance, a robot the size of a soft ball that is used to explore tight spaces underwater?

Capsid · 24th September 2004, 11:56 AM

I don't think this will work because as you scale up there is a weight issue and the cilia will have to be very large to support their own weight. It's not a linear relationship.

The example I read used Arthur C Clarke's novel called The Fountains of Paradise in which he describes a space elevator. The problem with this is that the structure needed to support this would be very heavy and hence collapse under its own weight. We don't have materials yet that are both strong and light enough.

Johnny Pneumatic · 24th September 2004, 12:08 PM

Quote:

Originally posted by Capsid
We don't have materials yet that are both strong and light enough.

Yeah we do. They just currently cost $300 to make a gram of it.(hint: it's carbon nanotubes; a.k.a. fullerene tubes)

Johnny Pneumatic · 24th September 2004, 12:48 PM

Quote:

Originally posted by Capsid
[b]I don't think this will work because as you scale up there is a weight issue and the cilia will have to be very large to support their own weight.

Why would they have to support their own weight? The hypothetical robot is in water and has gas cells inside it so it can vary its buoyancy from positive to negative. The cilia are for steering and rapidly changing depth.

Capsid · 25th September 2004, 04:09 AM

Yes, you have a point, the bouyancy would certainly help. But it's still a mass/inertia problem. As the robot gets bigger it has more mass and a thin rope like propulsion unit may not exert enough force to overcome inertia.

Why did this method of propulsion not appear in the evolution in higher organisms? Large animals all use paddles for propulsion.

Goshawk · 25th September 2004, 06:23 AM

But maybe that's only because organisms are under pressure to evolve the most efficient means of propulsion, and maybe it's just that cilia wouldn't be the most efficient means of propulsion for a large organism like, say, a fish, and so no fish have evolved them.

I'm visualizing a fish propelled by cilia: I think it would work, but it would be verrr....rrryyyy...sloooooooooow.... Mass will yield eventually to even the feeblest propulsion, it just takes a while--look at barges on the Mississippi river, they're being pushed by tugboats with relatively small engines (compared to something like an aircraft carrier). The tugboat that went under the bridge was designed to push six barges with a total of 24 million pounds of cargo. It's all about momentum, and being patient.

And any organism that was using cilia for propulsion would have to also evolve some kind of defense system for predators, since "speedy escape" wouldn't be an option. Possibly either a shell like a turtle, or toxicity of some kind.

I don't think that any large organism that was any shape other than totally streamlined would have a hope of making cilia propulsion work.

Even water turtles are streamlined, if you think about it. At least, they're *more* streamlined than box turtles.

SGT · 28th September 2004, 12:25 PM

There is a problem in scaling that was not mentioned:
The mass is proportional to the cube of the dimension, while the propulsion force obtained by a vibrating paddle (or cilion) is proportional to its surface (the square of the dimension).
That's why big animals use fins instead of cilia.

24th September 2004, 08:23 AM	#1
Johnny Pneumatic Corpuscle Clay Join Date: Oct 2003 Posts: 2,089	Scale and Cilia I'm quite fascinated by ciliated microorganisms. They are like little jet fighters underwater. Question: Can cilia be scaled up and still work like they do at micrometer scales? For instance, a robot the size of a soft ball that is used to explore tight spaces underwater?
	__________________ If we don't play god, who will?-James Watson What the hell is the matter with you people? Get your minds into the gutter!-Dorian Gray Good Lord - I've heard about this - cat juggling! Stop! Stop! Stop it! Stop it! Stop it! Good. Father, could there be a God that would let this happen?- Navin R. Johnson, The Jerk There is nothing to believe in. There's no need to believe...There is nothing to believe in in this world. -Vicious, Cowboy Bebop

24th September 2004, 11:56 AM	#2
Capsid Graduate Poster Join Date: Apr 2004 Posts: 1,507	I don't think this will work because as you scale up there is a weight issue and the cilia will have to be very large to support their own weight. It's not a linear relationship. The example I read used Arthur C Clarke's novel called The Fountains of Paradise in which he describes a space elevator. The problem with this is that the structure needed to support this would be very heavy and hence collapse under its own weight. We don't have materials yet that are both strong and light enough.
Capsid Graduate Poster Join Date: Apr 2004 Posts: 1,507

24th September 2004, 12:08 PM	#3
Johnny Pneumatic Corpuscle Clay Join Date: Oct 2003 Posts: 2,089	Quote: Originally posted by Capsid We don't have materials yet that are both strong and light enough. Yeah we do. They just currently cost $300 to make a gram of it.(hint: it's carbon nanotubes; a.k.a. fullerene tubes)
	__________________ If we don't play god, who will?-James Watson What the hell is the matter with you people? Get your minds into the gutter!-Dorian Gray Good Lord - I've heard about this - cat juggling! Stop! Stop! Stop it! Stop it! Stop it! Good. Father, could there be a God that would let this happen?- Navin R. Johnson, The Jerk There is nothing to believe in. There's no need to believe...There is nothing to believe in in this world. -Vicious, Cowboy Bebop

24th September 2004, 12:48 PM	#4
Johnny Pneumatic Corpuscle Clay Join Date: Oct 2003 Posts: 2,089	Quote: Originally posted by Capsid [b]I don't think this will work because as you scale up there is a weight issue and the cilia will have to be very large to support their own weight. Why would they have to support their own weight? The hypothetical robot is in water and has gas cells inside it so it can vary its buoyancy from positive to negative. The cilia are for steering and rapidly changing depth.
	__________________ If we don't play god, who will?-James Watson What the hell is the matter with you people? Get your minds into the gutter!-Dorian Gray Good Lord - I've heard about this - cat juggling! Stop! Stop! Stop it! Stop it! Stop it! Good. Father, could there be a God that would let this happen?- Navin R. Johnson, The Jerk There is nothing to believe in. There's no need to believe...There is nothing to believe in in this world. -Vicious, Cowboy Bebop

25th September 2004, 04:09 AM	#5
Capsid Graduate Poster Join Date: Apr 2004 Posts: 1,507	Yes, you have a point, the bouyancy would certainly help. But it's still a mass/inertia problem. As the robot gets bigger it has more mass and a thin rope like propulsion unit may not exert enough force to overcome inertia. Why did this method of propulsion not appear in the evolution in higher organisms? Large animals all use paddles for propulsion.
Capsid Graduate Poster Join Date: Apr 2004 Posts: 1,507

25th September 2004, 06:23 AM	#6
Goshawk Graduate Poster Join Date: Jan 2003 Location: Decatur, Illinois, USA Posts: 1,453	But maybe that's only because organisms are under pressure to evolve the most efficient means of propulsion, and maybe it's just that cilia wouldn't be the most efficient means of propulsion for a large organism like, say, a fish, and so no fish have evolved them. I'm visualizing a fish propelled by cilia: I think it would work, but it would be verrr....rrryyyy...sloooooooooow.... Mass will yield eventually to even the feeblest propulsion, it just takes a while--look at barges on the Mississippi river, they're being pushed by tugboats with relatively small engines (compared to something like an aircraft carrier). The tugboat that went under the bridge was designed to push six barges with a total of 24 million pounds of cargo. It's all about momentum, and being patient. And any organism that was using cilia for propulsion would have to also evolve some kind of defense system for predators, since "speedy escape" wouldn't be an option. Possibly either a shell like a turtle, or toxicity of some kind. I don't think that any large organism that was any shape other than totally streamlined would have a hope of making cilia propulsion work. Even water turtles are streamlined, if you think about it. At least, they're more streamlined than box turtles.

28th September 2004, 12:25 PM	#7
SGT Critical Thinker Join Date: Apr 2004 Location: Rio de Janeiro Posts: 345	There is a problem in scaling that was not mentioned: The mass is proportional to the cube of the dimension, while the propulsion force obtained by a vibrating paddle (or cilion) is proportional to its surface (the square of the dimension). That's why big animals use fins instead of cilia.
	__________________ Never attribute to malice that which can be adequately explained by stupidity. Hanlon's Razor Heaven, n. A place where the wicked cease from troubling you with talk of their personal affairs, and the good listen with attention while you expound on your own. A. Bierce